1. Field of the Invention
The instant invention generally relates to an improved process for producing di-(N,N-disubstituted amino) alkane compounds directly from a tertiary amino alkanol and a secondary amine compound; and more particularly, to an improved selective liquid phase process for directly producing a di-(N,N-disubstituted amino) alkane compound in the presence of certain specific catalytically effective substances.
2. Prior Art
Di-(N,N-disubstituted amino) alkanes are generally well-known compounds. These compounds have established utility as polyurethane catalysts, epoxy curing agents and as intermediates in the preparation of corrosion inhibitors, pharmaceuticals, emulsifiers, textile chemicals, rubber chemicals and the like. For example see Doyle, E. N., The Development and Use of Poly Urethane Products, McGraw-Hill Book Co., 1971, page 69. A specific class of these compounds, being the N,N'-dimorpholino alkanes, is an especially preferred polyurethane catalyst. Generally, this class is useful in catalyzing urethane systems including the C-lower alkyl substituted N,N'-dimorpholino alkane compounds wherein one or both of the morpholine moieties contain C-(substituted) lower alkyl radicals on one or more of the carbon atoms and/or wherein the alkane moiety is either a branched or straight chain divalent radical containing from 1 to about 10 carbon atoms. Corresponding compounds containing a single morpholino moiety, such as 4-(2-dimethylaminoethyl)morpholine also are useful as polyurethane catalysts. The di-(N,N-disubstituted amino) alkanes are well-known as shown in U.S. Pat. No. 3,121,115.
Di-(N,N-disubstituted amino) alkanes have generally been prepared by methods involving halogenated reactants or intermediates. For example, in one method, N-(2-chloroethyl) morpholine is reacted with morpholine. Such methods of preparation are unsatisfactory in that the halogenated reactants are not readily available, and the methods involve caustic neutralization of the product and the concomitant disposal of polluting by-products, such as the alkali halide salts. Ditertiary amino alkanes have been prepared non-catalytically notably by heating the tertiary amino alkanol and the secondary amine with an acid condensing agent in a quantity such that the acid is present in at least the molar equivalent of the amino alkanol.
In addition, there are procedures described in the literature for preparing N-alkylated amines in the presence of various catalysts. For example, it is known that metal phosphates catalyze the alkylation of amines, such as morpholine, with an alkyleneimine. For example, see U.S. Pat. No. 3,527,757. Additionally, it is disclosed in U.S. Pat. No. 3,843,648 that N-aminoalkylated morpholines are produced by the condensation of N,N-dimethylaminoethanol and morpholine in vapor phase in the presence of AlPO.sub.4 catalyst or a silica-alumina cracking catalyst at temperatures of 200.degree. C. to 400.degree. C. However, as disclosed in this reference, the selectivities to the desired product make the process particularly commercially unattractive. This is especially true when the conversion of the limiting reactant approaches 100%.
Additionally, it has been disclosed that certain phosphoric acid compounds are effective as catalysts in promoting condensation reactions between several types of amines and aminoalkanols which are carried out under relatively mild liquid phase processing conditions. For example, U.S. Pat. No. 3,121,115 to Meuly teaches a process for aminoalkylating certain amines having a replaceable amino hydrogen, particularly aromatic primary and secondary amines, which includes heating the amine compound with a N-tertiary aminoalkanol at from 150.degree. C. to 250.degree. C. in liquid phase with continuous water removal in the presence of a phosphoric acid compound such as aqueous or anhydrous orthophosphoric acid, phosphorus pentoxide or an alkyl phosphoric acid. Although this reference discloses homogeneous phosphorus dehydration catalysts, the selectivities, conversions and reaction times teach the process as particularly undesirable for commercial processes. Further use of the homogeneous catalyst requires separation of catalyst from he homogeneous product. The disclosed process requires long reaction times.
Therefore, a process having high selectivity at high conversion rates would be commercially advantageous. Unexpectedly, such a process has been inadvertantly discovered. Importantly, the discovered process does not share the drawbacks of vapor phase or those associated with homogeneous catalyst recovery. Specifically, di-(N,N-disubstituted amino) alkanes can be produced with unexpectedly high selectivity in liquid phase at temperatures above about 250.degree. C. in the presence of a heterogeneous alumina phosphate catalyst. Surprisingly, it has been found that the rather severe reaction conditions of the instant process facilitate product formation without the expected decomposition and formation of excessive by-products. Thus, selectivity is unexpected and surprising while activity is comparable to other well known processes. The limiting reactant can be recycled to accomplish a substantially 100% yield of the desired product, a result heretofore taught in the art as unachievable. The instant process does not require an expensive neutralization step nor is it attended by vapor phase reaction deficiencies such as vaporizing the reactants, low conversion rates, low selectivities, catalyst deactivation and the like. The catalyst is also heterogeneous, eliminating costly separation problems.